Adds documentation for release 2.31

Author: ademariag

docs/notes/2.31.x.md

@@ -29,6 +29,9 @@ pantsd now preserves web proxy environment variables (`HTTP_PROXY`, `HTTPS_PROXY
 
 ### Backends
 
+#### Docker
+[Fixed](https://github.com/pantsbuild/pants/issues/22575) a bug that would make docker hashes unstable when using dynamic tags.
+
 #### Helm
 
 #### JVM